Unitary medical sensor assembly and technique for using the same

ABSTRACT

A sensor assembly is provided that includes a frame having a first portion and a second portion connected by a hinge. An emitter and a detector are disposed on the frame. A coating is provided over the frame, the emitter and the detector to form a unitary sensor assembly. The sensor assembly also includes a resistance-providing component disposed generally about the hinge. In one embodiment, the sensor assembly may be placed on a patient&#39;s finger, toe, ear, and so forth to obtain pulse oximetry or other physiological measurements. A method of manufacturing the sensor assembly is also provided as is a method of cleaning a fluid-tight sensor assembly.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation of U.S. application Ser. No.11/199,525 filed Aug. 8, 2005, the disclosure of which is herebyincorporated by reference in its entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates generally to medical devices and, moreparticularly, to sensors used for sensing physiological parameters of apatient.

2. Description of the Related Art

This section is intended to introduce the reader to various aspects ofart that may be related to various aspects of the present invention,which are described and/or claimed below. This discussion is believed tobe helpful in providing the reader with background information tofacilitate a better understanding of the various aspects of the presentinvention. Accordingly, it should be understood that these statementsare to be read in this light, and not as admissions of prior art.

In the field of medicine, doctors often desire to monitor certainphysiological characteristics of their patients. Accordingly, a widevariety of devices have been developed for monitoring physiologicalcharacteristics. Such devices provide doctors and other healthcarepersonnel with the information they need to provide the best possiblehealthcare for their patients. As a result, such monitoring devices havebecome an indispensable part of modern medicine.

One technique for monitoring certain physiological characteristics of apatient is commonly referred to as pulse oximetry, and the devices builtbased upon pulse oximetry techniques are commonly referred to as pulseoximeters. Pulse oximetry may be used to measure various blood flowcharacteristics, such as the blood-oxygen saturation of hemoglobin inarterial blood, the volume of individual blood pulsations supplying thetissue, and/or the rate of blood pulsations corresponding to eachheartbeat of a patient.

Pulse oximeters typically utilize a non-invasive sensor that is placedon or against a patient's tissue that is well perfused with blood, suchas a patient's finger, toe, forehead or earlobe. The pulse oximetersensor emits light and photoelectrically senses the absorption and/orscattering of the light after passage through the perfused tissue. Thedata collected by the sensor may then be used to calculate one or moreof the above physiological characteristics based upon the absorption orscattering of the light. More specifically, the emitted light istypically selected to be of one or more wavelengths that are absorbed orscattered in an amount related to the presence of oxygenated versusde-oxygenated hemoglobin in the blood. The amount of light absorbedand/or scattered may then be used to estimate the amount of the oxygenin the tissue using various algorithms.

In many instances, it may be desirable to employ, for cost and/orconvenience, a pulse oximeter sensor that is reusable. Such reusablesensors, however, may be uncomfortable for the patient for variousreasons. For example, the materials used in their construction may notbe adequately compliant or supple or the structural features may includeangles or edges.

Furthermore, the reusable sensor should fit snugly enough thatincidental patient motion will not dislodge or move the sensor, yet notso tight that it may interfere with pulse oximetry measurements. Such aconforming fit may be difficult to achieve over a range of patientphysiologies without adjustment or excessive attention on the part ofmedical personnel. In addition, lack of a tight or secure fit may allowlight from the environment to reach the photodetecting elements of thesensor. Such environmental light is not related to a physiologicalcharacteristic of the patient and may, therefore, introduce error intothe measurements derived using data obtained with the sensor.

Reusable pulse oximeter sensors are also used repeatedly and, typically,on more than one patient. Therefore, over the life of the sensor,detritus and other bio-debris (sloughed off skin cells, dried fluids,dirt, and so forth) may accumulate on the surface of the sensor or increvices and cavities of the sensor, after repeated uses. As a result,it may be desirable to quickly and/or routinely clean the sensor in athorough manner. However, in sensors having a multi-part construction,as is typical in reusable pulse oximeter sensors, it may be difficult toperform such a quick and/or routine cleaning. For example, such athorough cleaning may require disassembly of the sensor and individualcleaning of the disassembled parts or may require careful cleaning usingutensils capable of reaching into cavities or crevices of the sensor.Such cleaning is labor intensive and may be impractical in a typicalhospital or clinic environment.

SUMMARY

Certain aspects commensurate in scope with the originally claimedinvention are set forth below. It should be understood that theseaspects are presented merely to provide the reader with a brief summaryof certain forms of the invention might take and that these aspects arenot intended to limit the scope of the invention. Indeed, the inventionmay encompass a variety of aspects that may not be set forth below.

There is provided a sensor assembly that includes: a frame comprising afirst portion and a second portion connected by a hinge; an emitterdisposed on the frame; a detector disposed on the frame; a coatingprovided over the frame, the emitter, and the detector to form a unitarysensor assembly; and a resistance-providing component disposed generallyabout the hinge.

There is also provided a method of manufacturing a sensor that includes:positioning an emitter and detector relative to a frame comprising afirst portion and a second portion connected by a hinge; and coating theframe, the emitter, and the detector to form a unitary sensor assembly.

There is also included a method for cleaning a sensor assembly thatincludes: immersing or rinsing a fluid-tight sensor assembly in at leastone of water or a disinfectant, wherein electrical and opticalcomponents of the fluid-tight sensor assembly are not exposed to thewater or the disinfectant during the immersion or rinse.

BRIEF DESCRIPTION OF THE DRAWINGS

Advantages of the invention may become apparent upon reading thefollowing detailed description and upon reference to the drawings inwhich:

FIG. 1 illustrates a patient monitoring system coupled to amulti-parameter patient monitor and a bi-stable sensor, in accordancewith aspects of the present technique;

FIG. 2 illustrates a closed internal frame for use in a bi-stablesensor, in accordance with aspects of the present technique;

FIG. 3 illustrates a side view of the internal frame of FIG. 2 in anopen configuration;

FIG. 4 illustrates a side view of the internal frame of FIG. 2 in aclosed configuration;

FIG. 5A illustrates a side view of the internal frame of FIG. 2 in aclosed configuration with an elastic band disposed about the hingeregion;

FIG. 5B illustrates a side view of the internal frame of FIG. 2 in anopen configuration with an elastic band disposed about the hinge region;

FIG. 6 illustrates an overmolded bi-stable sensor, in accordance withaspects of the present technique;

FIG. 7 illustrates the overmolded bi-stable sensor of FIG. 6 in an openconfiguration;

FIG. 8 illustrates the bi-stable sensor of FIG. 6 in use on a patient'sfinger, in accordance with aspects of the present technique;

FIG. 9 illustrates a cross-section taken along section line 9 of FIG. 6;and

FIG. 10 illustrates a cross-section taken along section line 10 of FIG.6.

DETAILED DESCRIPTION OF SPECIFIC EMBODIMENTS

One or more specific embodiments of the present invention will bedescribed below. In an effort to provide a concise description of theseembodiments, not all features of an actual implementation are describedin the specification. It should be appreciated that in the developmentof any such actual implementation, as in any engineering or designproject, numerous implementation-specific decisions must be made toachieve the developers' specific goals, such as compliance withsystem-related and business-related constraints, which may vary from oneimplementation to another. Moreover, it should be appreciated that sucha development effort might be complex and time consuming, but wouldnevertheless be a routine undertaking of design, fabrication, andmanufacture for those of ordinary skill having the benefit of thisdisclosure.

It is desirable to provide a comfortable and conformable reusablepatient sensor, such as for use in pulse oximetry or other applicationsutilizing spectrophotometry, that is easily cleaned and that isresistant to environmental light infiltration. In accordance with someaspects of the present technique, a reusable patient sensor is providedthat is overmolded to provide patient comfort and a suitably conformablefit. The overmold material provides a seal against bodily fluids, aswell as water or other cleaning fluids, that allows easy cleaningwithout disassembly or special tools.

In accordance with some aspects of the present technique, the reusablepatient sensor has more than one mechanically stable configuration, suchas two-stable configurations, in a mechanically bi-stableimplementation. As will be appreciated by those of ordinary skill in theart, such multi- or bi-stable configurations are resistant totransitions or movement between stable configurations, therefore eachconfiguration is stable absent an applied force sufficient to overcomethis resistance. In this way, a bi-stable device in one of its stableconfigurations will remain in that stable configuration until a force isapplied to overcome the resistance to the transition to the secondstable configuration. Once such a force is applied, however, and thebi-stable device is in the second stable configuration, the resistancenow functions to resist transition back to the first stableconfiguration. For example, for a bi-stable sensor having open andclosed configurations, the sensor will remain open until sufficientforce is applied to close the sensor, however, once closed, the sensorwill remain closed absent a second application of force sufficient tore-open the sensor.

Prior to discussing such exemplary multi- or bi-stable sensors indetail, it should be appreciated that such sensors may be designed foruse with a typical patient monitoring system. For example, referring nowto FIG. 1, a bi-stable sensor 10 according to the present invention maybe used in conjunction with a patient monitor 12. In the depictedembodiment, a cable 14 connects the bi-stable sensor 10 to the patientmonitor 12. As will be appreciated by those of ordinary skill in theart, the sensor 10 and/or the cable 14 may include or incorporate one ormore integrated circuit devices or electrical devices, such as a memory,processor chip, or resistor, that may facilitate or enhancecommunication between the bi-stable sensor 10 and the patient monitor12. Likewise the cable 14 may be an adaptor cable, with or without anintegrated circuit or electrical device, for facilitating communicationbetween the bi-stable sensor 10 and various types of monitors, includingolder or newer versions of the patient monitor 12 or other physiologicalmonitors. In other embodiments, the bi-stable sensor 10 and the patientmonitor 12 may communicate via wireless means, such as using radio,infrared, or optical signals. In such embodiments, a transmission device(not shown) may be connected to the bi-stable sensor 10 to facilitatewireless transmission between the bi-stable sensor 10 and the patientmonitor 12. As will be appreciated by those of ordinary skill in theart, the cable 14 (or corresponding wireless transmissions) aretypically used to transmit control or timing signals from the monitor 12to the bi-stable sensor 10 and/or to transmit acquired data from thebi-stable sensor 10 to the monitor 12. In some embodiments, however, thecable 14 may be an optical fiber that allows optical signals to beconducted between the monitor 12 and the bi-stable sensor 10.

In one embodiment, the patient monitor 12 may be a suitable pulseoximeter, such as those available from Nellcor Puritan Bennett Inc. Inother embodiments, the patient monitor 12 may be a monitor suitable formeasuring tissue water fractions, or other body fluid related metrics,using spectrophotometric or other techniques. Furthermore, the monitor12 may be a multi-purpose monitor suitable for performing pulse oximetryand measurement of tissue water fraction, or other combinations ofphysiological and/or biochemical monitoring processes, using dataacquired via the sensor 10. Furthermore, to upgrade conventionalmonitoring functions provided by the monitor 12 to provide additionalfunctions, the patient monitor 12 may be coupled to a multi-parameterpatient monitor 16 via a cable 18 connected to a sensor input portand/or via a cable 20 connected to a digital communication port.

The sensor 10, in the example depicted in FIG. 1, is a bi-stable sensorthat is overmolded to provide a unitary or enclosed assembly. Thebi-stable sensor 10 includes an emitter 22 and a detector 24 which maybe of any suitable type. For example, the emitter 22 may be one or morelight emitting diodes adapted to transmit one or more wavelengths oflight, such as in the red to infrared range, and the detector 24 may bea photodetector, such as a silicon photodiode package, selected toreceive light in the range emitted from the emitter 22. In the depictedembodiment, the bi-stable sensor 10 is coupled to a cable 14 that isresponsible for transmitting electrical and/or optical signals to andfrom the emitter 22 and detector 24 of the bi-stable sensor 10. Thecable 14 may be permanently coupled to the bi-stable sensor 10, or itmay be removably coupled to the bi-stable sensor 10—the latteralternative being more useful and cost efficient in situations where thebi-stable sensor 10 is disposable.

The bi-stable sensor 10 described above is generally configured for useas a “transmission type” sensor for use in spectrophotometricapplications, though in some embodiments it may instead be configuredfor use as a “reflectance type sensor.” Transmission type sensorsinclude an emitter and detector that are typically placed on opposingsides of the sensor site. If the sensor site is a fingertip, forexample, the bi-stable sensor 10 is positioned over the patient'sfingertip such that the emitter and detector lie on either side of thepatient's nail bed. For example, the bi-stable sensor 10 is positionedso that the emitter is located on the patient's fingernail and thedetector is located opposite the emitter on the patient's finger pad.During operation, the emitter shines one or more wavelengths of lightthrough the patient's fingertip, or other tissue, and the light receivedby the detector is processed to determine various physiologicalcharacteristics of the patient.

Reflectance type sensors generally operate under the same generalprinciples as transmittance type sensors. However, reflectance typesensors include an emitter and detector that are typically placed on thesame side of the sensor site. For example, a reflectance type sensor maybe placed on a patient's fingertip such that the emitter and detectorare positioned side-by-side. Reflectance type sensors detect lightphotons that are scattered back to the detector.

For pulse oximetry applications using either transmission or reflectancetype sensors the oxygen saturation of the patient's arterial blood maybe determined using two or more wavelengths of light, most commonly redand near infrared wavelengths. Similarly, in other applications a tissuewater fraction (or other body fluid related metric) or a concentrationof one or more biochemical components in an aqueous environment may bemeasured using two or more wavelengths of light, most commonly nearinfrared wavelengths between about 1,000 nm to about 2,500 nm. It shouldbe understood that, as used herein, the term “light” may refer to one ormore of infrared, visible, ultraviolet, or even X-ray electromagneticradiation, and may also include any wavelength within the infrared,visible, ultraviolet, or X-ray spectra.

Pulse oximetry and other spectrophotometric sensors, whethertransmission-type or reflectance-type, are typically placed on a patientin a location conducive to measurement of the desired physiologicalparameters. For example, pulse oximetry sensors are typically placed ona patient in a location that is normally perfused with arterial blood tofacilitate measurement of the desired blood characteristics, such asarterial oxygen saturation measurement (SaO₂). Common pulse oximetrysensor sites include a patient's fingertips, toes, forehead, orearlobes. Regardless of the placement of the bi-stable sensor 10, thereliability of the pulse oximetry measurement is related to the accuratedetection of transmitted light that has passed through the perfusedtissue and has not been inappropriately supplemented by outside lightsources or modulated by subdermal anatomic structures. Suchinappropriate supplementation and/or modulation of the light transmittedby the sensor can cause variability in the resulting pulse oximetrymeasurements.

As noted above, the bi-stable sensor 10 discussed herein may beconfigured for either transmission or reflectance type sensing. Forsimplicity, the exemplary embodiment of the bi-stable sensor 10described herein is adapted for use as a transmission-type sensor. Aswill be appreciated by those of ordinary skill in the art, however, suchdiscussion is merely exemplary and is not intended to limit the scope ofthe present technique.

Referring now to FIGS. 2-5, an internal frame 30 for a bi-stable sensor10 is depicted. In the depicted example, the internal frame 30 is askeletal frame for a bi-stable sensor 10. Such a skeletal frame mayinclude different structures or regions that may or may not have similarrigidities. For example, the depicted skeletal frame includes structuralsupports 34 that define the general shape of the sensor 10 when coated,as discussed below with regard to FIGS. 6-10. In view of their structureproviding function, the structural supports 34 may be constructed to besubstantially rigid or semi-rigid. In addition, the skeletal frame mayinclude a cable guide 36 through which a cable, such as an electrical oroptical cable, may pass to connect to the electrical or opticalconductors attached to the emitter 22 and/or detector 24 upon assembly.Likewise, a skeletal frame, such as the depicted internal frame 30, mayinclude component housings, such as the emitter housing 38 and detectorhousing 40 and struts 42 attaching such housings to the remainder of theskeletal frame. The struts 42 may be relatively flexible, allowing theemitter housing 38 and/or the detector housing 40 to move vertically(such as along an optical axis between the respective housings) relativeto the structural supports 34 of the skeletal frame. Alternatively, inembodiments where the struts 42 are relatively rigid, where multiplestruts 42 are employed to attach the housings 38 and 40 to thestructural supports 34, or where the internal frame is substantiallysolid instead of skeletal, the housings 38 and/or 40 may be fixedrelative to the respective structural supports 34 and, therefore, movewith the structural supports 34.

In embodiments where the internal frame 30 is skeletal, the variousstructural supports 34, housings 38 and 40, struts 42, and otherstructures may define various openings and spaces between and/or aroundthe structures of the skeletal frame. In this manner, the skeletal frameprovides structural support at specific locations for a coating orovermolding. However, in regions where structural support is notprovided, flexibility and freedom of motion in an overlying coating orovermolding may be possible. For example, in one implementation, theemitter housing 38 and/or the detector housing 40 may be attached to theremainder of the skeletal frame by flexible struts 42, as depicted inFIG. 2. In such implementations, a coating provided proximate to theemitter housing 38 and/or detector housing 40 may be sufficientlyflexible (such as due to the elasticity and/or the thinness of thecoating material in the open areas of the skeletal frame) such that thehousings 38 and 40 may move independent of the structural supports 34 ofthe frame 30 along an optical axis between the housings 38 and 40.

In certain embodiments, the internal frame 30 is constructed, in wholeor in part, from polymeric materials, such as thermoplastics, capable ofproviding a suitable rigidity or semi-rigidity for the differentportions of the internal frame 30. Examples of such suitable materialsinclude polyurethane, polypropylene and nylon, though other polymericmaterials may also be suitable. In other embodiments, the internal frame30 is constructed, in whole or in part, from other suitably rigid orsemi-rigid materials, such as stainless steel, aluminum, magnesium,graphite, fiberglass, or other metals, alloys, or compositions that aresufficiently ductile and/or strong. For example, metals, alloys, orcompositions that are suitable for diecasting, sintering, lost waxcasting, stamping and forming, and other metal or compositionfabrication processes may be used to construct the internal frame 30.

In addition, the internal frame 30 may be constructed as an integralstructure or as a composite structure. For example, in one embodiment,the internal frame 30 may be constructed as a single piece from a singlematerial or from different materials. Alternatively, the internal frame30 may be constructed or assembled from two or more parts that areseparately formed. In such embodiments, the different parts may beformed from the same or different materials. For example, inimplementations where different parts are formed from differentmaterials, each part may be constructed from a material having suitablemechanical and/or chemical properties for that part. The different partsmay then be joined or fitted together to form the internal frame 30.

In addition, the internal frame 30 may be molded, formed, or constructedin a different configuration than the final sensor configuration. Forexample, the internal frame 30 for use in the bi-stable sensor 10 may beinitially formed in a generally open, or flat, configuration, asdepicted in FIG. 3. The internal frame 30 may then be bent from the openconfiguration into a relatively closed configuration, as depicted inFIG. 4.

In certain embodiments, the internal frame 30 is fitted with aresistance component, such as an elastic band 50 fitted about a hingeregion 52, as depicted in FIGS. 5A and 5B. The resistance componentprovides or augments a resistance to transitions between configurationsof the bi-stable sensor 10, as depicted generally by arrows generallyindicative of the direction force (F) is applied by the resistancecomponent. That is, the resistance provided or augmented by theresistance component is overcome to transition between two mechanicallystable sensor configurations. For example, in FIG. 5A, the resistancecomponent provides force, F, that biases a first portion 54 and a secondportion 56 of the internal frame 30 closed absent a greater opposingforce, i.e., an opening force. Likewise, in FIG. 5B, the resistancecomponent provides force, F, that biases the first portion 54 and secondportion 56 of the internal frame 30 apart absent a greater opposingforce, i.e., a closing force.

As will be appreciated by those of ordinary skill in the art, aresistance component, such as elastic band 50, may be composed of amaterial or a combination of materials that provide the desiredelasticity and resistance, such as polymeric materials (rubber, plastic,and so forth) or metals. Likewise, the resistance component may takeother forms than a continuous loop, such as the exemplary elastic band50. For example, an elastic band or strap may be configured withdove-tailed ends or with a dog-bone shape to facilitate connection tothe frame 30, such as to conform to complementary attachment regionsintegral to the frame 30.

Though the present example depicts the resistance component, in the formof elastic band 50, as being disposed directly on the frame 30, one ofordinary skill in the art will appreciate that other configurations arealso possible. For example, the resistance component, such as elasticband 50, may be disposed within a coating material overlying the frame30 or external to such a coating material. Similarly, in otherembodiments, the resistance component may be provided as part of theframe 30, such as a hinge portion 52 configured to resist transitionsbetween stable configurations (without augmentation by an addedresistance component). Likewise, the resistance component may be or mayinclude an elastomeric coating material, as discussed below, disposedover the frame 30. In such embodiments, the coating material may providethe resistance based on the elasticity or other physical properties ofthe coating material itself. Alternatively, the resistance provided bythe coating may be based on regions of the coating that differ inelasticity and/or hardness, thereby forming resistive structures orregions within the coating.

As noted above, in certain embodiments of the present technique, theframe 30 (such as a skeletal, internal frame) is coated to form aunitary or integral sensor assembly, as depicted in FIGS. 6-10. Suchovermolded embodiments may result in a sensor assembly in which theinternal frame 30 is completely or substantially coated. In embodimentsin which the internal frame 30 is formed or molded as a relatively openor flat structure, the overmolding or coating process may be performedprior to or subsequent to bending the internal frame 30 into the closedconfiguration.

For example, the bi-stable sensor 10 may be formed by an injectionmolding process. In one example of such a process the internal frame 30,with or without an attached elastic band 50, may be positioned within adie or mold of the desired shape for the bi-stable sensor 10. A moltenor otherwise unset overmold material may then be injected into the dieor mold. For example, in one implementation, a molten thermoplasticelastomer at between about 400° F. to about 450° F. is injected into themold. The overmold material may then be set, such as by cooling for oneor more minutes or by chemical treatment, to form the sensor body aboutthe internal frame 30 and the elastic band 50, if present. In certainembodiments, other sensor components, such as the emitter 22 and/ordetector 24, may be attached or inserted into their respective housingsor positions on the overmolded sensor body.

Alternatively, the optical components (such as emitter 22 and detector24) and/or conductive structures (such as wires or flex circuits) may beplaced on the internal frame 30 prior to overmolding. The internal frame30 and associated components may then be positioned within a die or moldand overmolded, as previously described. To protect the emitter 22,detector 24, and or other electrical components, conventional techniquesfor protecting such components from excessive temperatures may beemployed. For example, the emitter 22 and/or the detector 24 may includean associated clear window, such as a plastic or crystal window, incontact with the mold to prevent coating from being applied over thewindow. In one embodiment, the material in contact with such windows maybe composed of a material, such as beryllium copper, which prevents theheat of the injection molding process from being conveyed through thewindow to the optical components. For example, in one embodiment, aberyllium copper material initially at about 40° F. is contacted withthe windows associated with the emitter 22 and/or detector 24 to preventcoating of the windows and heat transfer to the respective opticalcomponents. As will be appreciated by those of ordinary skill in theart, the injection molding process described herein is merely onetechnique by which the frame 30 may be coated to form a sensor body,with or without associated sensing components. Other techniques whichmay be employed include, but are not limited to, dipping the frame 30into a molten or otherwise unset coating material to coat the frame 30or spraying the frame 30 with a molten or otherwise unset coatingmaterial to coat the frame 30. In such implementations, the coatingmaterial may be subsequently set, such as by cooling or chemical means,to form the coating. Such alternative techniques, to the extent thatthey may involve high temperatures, may include thermally protectingwhatever optical components are present, such as by using berylliumcopper or other suitable materials to prevent heat transfer through thewindows associated with the optical components, as discussed above.

By such techniques, the frame 30, as well as the optical components andassociated circuitry where desired, may be encased in a coating material60 to form an integral or unitary assembly with no exposed or externalmoving parts of the frame 30. For example, as depicted in FIGS. 6 and 7,the bi-stable sensor 10 includes features of the underlying internalframe 30 that are now completely or partially overmolded, such as theovermolded emitter housing 62 and detector housing 64. In addition, theovermolded bi-stable sensor 10 includes an overmolded upper portion 70and lower portion 72 that may be fitted to the finger, toe, ear, orother appendage of a patient when the bi-stable sensor 10 is in a closedconfiguration.

In one implementation, the overmolding or coating 60 is a thermoplasticelastomer or other conformable coating or material. In such embodiments,the thermoplastic elastomer may include compositions such asthermoplastic polyolefins, thermoplastic vulcanizate alloys, silicone,thermoplastic polyurethane, and so forth. As will be appreciated bythose of ordinary skill in the art, the overmolding composition mayvary, depending on the varying degrees of conformability, durability,wettability, elasticity, or other physical and/or chemical traits thatare desired.

Furthermore, the coating material 60 may be selected or configured toprovide some or all of the resistance to transitions of the bi-stablesensor 10 between open and closed configurations, as depicted in FIGS. 6and 7. For example, referring now to FIGS. 6 and 7, the coating material60 may be disposed as a thick region 74 or layer about the hinge regionof the bi-stable sensor (generally corresponding to the overmolded hingeregion 52 of the frame 30). In this manner, the thickness of the thickregion 74 and the elasticity of the coating material 60 may provideresistance, indicated by force arrows, F, which opposes transitionsbetween different configurations of the bi-stable sensor 10. Forexample, as depicted in FIG. 7, in an open configuration, the resistanceprovided by the thick region 74 of coating material acts to bias theupper portion 70 and lower portion 72 of the sensor body 10 apart. Asufficient opposing or closing force, however, may overcome theresistance provided by the thick region 74 of coating material, totransition the sensor body 10 a closed configuration, as depicted inFIG. 6. Once in the closed configuration, the thick region 74 of coatingmaterial then resists transition to the open configuration, as indicatedby force arrows, F, in FIG. 6. As will be appreciated by those ofordinary skill in the art, in the closed configuration, the upperportion 70 and lower portion 72 may be partially separated without fullyovercoming the resistance to transition, i.e., without “opening” thesensor 10, allowing the sensor 10 to be comfortably and conformablyfitted to a patient's finger 76, as depicted in FIG. 8, or to apatient's toe, ear, and so forth, in other embodiments.

The depicted sensor 10, therefore, has two mechanically stableconfigurations, i.e., it is bi-stable, with each stable configurationresisting change absent a force sufficient to overcome the resistanceprovided by the sensor itself. As will be appreciated by those ofordinary skill in the art, the resistance to transitioning betweenstable configurations may depend on various factors, such as thosedescribed by example herein. For example, to the extent that theresistance is provided at least partly by a thick region 74 of coatingmaterial, as depicted in FIGS. 6 and 7, the resistance may be a functionof the thickness of the thick region 74, the elasticity and/or hardnessof the coating material 60, and the presence of additional resistivestructure within or about the thick region 74. For instance, the thickregion 74 may be composed of coating material 60 having uniformcomposition, elasticity, hardness, and so forth. Alternatively, thethick region 74 may be composed of more than one type of coatingmaterial 60, with the different coating materials having differentelasticities, hardnesses, or other mechanical properties that affect theresistance to transition between stable configurations of the sensor 10.Furthermore, the thick region 74 of coating material may overlie,incorporate, or support an additional resistive structure, such as anelastic band 50 disposed about the hinge region 52 of the frame.Therefore, as will be appreciated by those of ordinary skill in the art,the resistance opposing transitions between stable configurations of thesensor 10 may be determined by a variety of factors, such as thethickness of the coating material 60 about a hinge of the sensor 10, thecomposition, configuration, and/or uniformity of the coating material 60about the hinge of the sensor 10, the construction or inclusion ofadditional resistive structures about the hinge of the sensor 10, aswell as other possible factors.

While selection of the coating material 60 may be based upon theresistance considerations noted above, the coating material 60 may alsobe selected based upon the desirability of a chemical bond between theinternal frame 30 and the coating material 60. Such a chemical bond maybe desirable for durability of the resulting overmolded bi-stable sensor10. For example, to prevent separation of the coating 60 from theinternal frame 30, the material used to form the coating 60 may beselected such that the coating 60 bonds with some or all of the internalframe 30 during the overmolding process. In such embodiments, thecoating 60 and the portions of the internal frame 30 to which thecoating 60 is bonded are not separable, i.e., they form one continuousand generally inseparable structure.

Furthermore, in embodiments in which the coating 60 employed is liquidor fluid tight, such a bi-stable sensor 10 may be easily maintained,cleaned, and/or disinfected by immersing the sensor into a disinfectantor cleaning solution or by rinsing the sensor 10 off, such as underrunning water. For example, in an open configuration of the sensor 10,as depicted in FIG. 7, and the sensor 10 may be immersed or rinsed withwater or a disinfectant solution for easy cleaning. Of course, thebi-stable sensor 10 may be cleaned in either the closed or openconfiguration. In particular, the overmolded bi-stable sensor 10 may begenerally or substantially free of crevices, gaps, junctions or othersurface irregularities typically associated with a multi-partconstruction which may normally allow the accumulation of biologicaldetritus or residue. Such an absence of crevices and otherirregularities may further facilitate the cleaning and care of thesensor 10.

Turning now to FIGS. 9 and 10, cross-sections of the coated bi-stablesensor 10 in a closed configuration are depicted taken throughtransverse optical planes, represented by section line 8 and 9 of FIG. 6respectively. FIGS. 8 and 9 depict, among other aspects of the bi-stablesensor 10, the overmolding material 60 as well as underlying portions ofthe internal frame 30, such as the emitter housing 38 and detectorhousing 40, along with the respective emitter 22, detector 24, andsignal transmission structures (such as wiring 82 or other structuresfor conducting electrical or optical signals). In the depictedembodiment, the emitter 22 and detector 24 are provided substantiallyflush with the patient facing surfaces of the bi-stable sensor 10, asmay be suitable for pulse oximetry applications. For other physiologicalmonitoring applications, such as applications measuring tissue waterfraction or other body fluid related metrics, other configurations maybe desirable. For example, in such fluid measurement applications it maybe desirable to provide one or both of the emitter 22 and detector 24recessed relative to the patient facing surfaces of the bi-stable sensor10. Such modifications may be accomplished by proper configuration ordesign of a mold or die used in overmolding the internal frame 30 and/orby proper design of the emitter housing 38 or detector housing 40 of theinternal frame 30.

In addition, as depicted in FIGS. 9 and 10, in certain embodimentsportions 86 of the coating material 60 may be flexible, such as thin ormembranous regions of coating material 60 disposed between structuralsupports 34 of a skeletal frame. Such flexible regions 86 allow agreater range of digit sizes to be accommodated for a given retention orclamping force of the sensor 10. For example, the flexible regions 86may allow the emitter 22 and/or detector 24, to flex or expand apartfrom one another along the optical axis in embodiments in which therespective housings 38 and 40 are flexibly attached to the remainder ofthe frame 30. In this manner, the sensor 10 may accommodate differentlysized digits. For instance, for a relatively small digit, the flexibleregions 86 may not be substantially deformed or vertically displaced,and therefore the emitter 22 and/or detector 24 are not substantiallydisplaced either. For larger digits, however, the flexible regions 86may be deformed or displaced to a greater extent to accommodate thedigit, thereby displacing the emitter 22 and/or detector 24 as well. Inaddition, for medium to large digits, the flexible regions 86 may alsoincrease retention of the sensor 10 on the digit by increasing thesurface area to which the retaining force is applied.

Furthermore, as the flexible regions 86 deform, the force applied to thedigit is spread out over a large area on the digit due to thedeformation of the flexible region 86. In this way, a lower pressure ondigits of all sizes may be provided for a given vertical force.Therefore, a suitable conforming fit may be obtained in which theemitter 22 and detector 24 are maintained in contact with the digitwithout the application of concentrated and/or undesirable amounts offorce, thereby improving blood flow through the digit.

In the example depicted in FIGS. 6-10, flaps or side extensions 88 ofthe coating material 60 on the sides of the bi-stable sensor 10 aredepicted which facilitate the exclusion of environmental or ambientlight from the interior of the bi-stable sensor 10. Such extensions helpprevent or reduce the detection of light from the outside environment,which may be inappropriately detected by the sensor 10 as correlating tothe SaO₂. Thus, the pulse oximetry sensor may detect differences insignal modulations unrelated to the underlying SaO₂ level. In turn, thismay impact the detected red-to-infrared modulation ratio and,consequently, the measured blood oxygen saturation (SpO₂) value. Theconformability of the fit of sensor 10 and the use of side extensions88, therefore, may help prevent or reduce such errors.

While the exemplary bi-stable sensors 10 discussed herein are someexamples of overmolded or coated medical devices, other such devices arealso contemplated and fall within the scope of the present disclosure.For example, other medical sensors and/or contacts applied externally toa patient may be advantageously applied using a bi-stable sensor body asdiscussed herein. Examples of such sensors or contacts may includeglucose monitors or other sensors or contacts that are generally heldadjacent to the skin of a patient such that a conformable andcomfortable fit is desired. Similarly, and as noted above, devices formeasuring tissue water fraction or other body fluid related metrics mayutilize a sensor as described herein. Likewise, other spectrophotometricapplications where a probe is attached to a patient may utilize a sensoras described herein.

In addition, overmolded bi-stable medical devices for use invasively,i.e., within the patient, are also presently contemplated. For example,clamps or other medical devices used invasively may be designed asbi-stable devices, i.e., having an open and a closed position, in whichthe transition between configurations is accomplished using asubstantial force, thereby preventing incidental or accidentaltransitions between open and closed configurations. Furthermore, anovermolding or other coating may be provided on such devices, such aswhere non-reactivity with bodily fluids or tissues is desired, or whereit is generally desired to provide an invasive device having few or noexposed niches or crevices or where it is generally desired to coat theinternal framework or skeleton of a device.

While the invention may be susceptible to various modifications andalternative forms, specific embodiments have been shown by way ofexample in the drawings and have been described in detail herein.However, it should be understood that the invention is not intended tobe limited to the particular forms disclosed. Rather, the invention isto cover all modifications, equivalents, and alternatives falling withinthe spirit and scope of the invention as defined by the followingappended claims. Indeed, the present techniques may not only be appliedto transmission type sensors for use in pulse oximetry, but also toretroflective and other sensor designs as well. Likewise, the presenttechniques are not limited to use on fingers and toes but may also beapplied to placement on other body parts such as in embodimentsconfigured for use on the ears or nose.

1. A sensor assembly, comprising: a frame comprising a first portion anda second portion connected by a hinge; an emitter disposed on the frame;a detector disposed on the frame; a coating molded over the frame, theemitter, and the detector to form a unitary sensor assembly; and aresistance-providing component disposed generally about the hinge. 2.The sensor assembly of claim 1, wherein the resistance-providingcomponent comprises one or more elastic bands disposed beneath thecoating.
 3. The sensor assembly of claim 1, wherein theresistance-providing component comprises one or more elastic bandsdisposed external to the coating.
 4. The sensor assembly of claim 1,wherein the resistance-providing component comprises one or more elasticbands disposed within the coating.
 5. The sensor assembly of claim 1,wherein the resistance-providing component comprises a region of thecoating.
 6. The sensor assembly of claim 1, wherein theresistance-providing component comprises a thick region of the coating.7. The sensor assembly of claim 1, comprising one or more signaltransmission structures connected to at least one of the emitter or thedetector.
 8. The sensor assembly of claim 1, wherein the unitary sensorassembly comprises at least one of a pulse oximetry sensor, a sensor formeasuring a water fraction, or a combination thereof.
 9. The sensorassembly of claim 1, wherein the frame comprises a single molded part.10. The sensor assembly of claim 1, wherein the frame comprises two ormore parts joined to form the frame.
 11. The sensor assembly of claim 1,wherein the resistance-providing component comprises at least one of apolymeric material or a metal.
 12. The sensor assembly of claim 1,wherein the coating comprises a thermoplastic elastomer.
 13. The sensorassembly of claim 12, wherein the thermoplastic elastomer comprises atleast one of a thermoplastic polyolefin, a thermoplastic vulcanizatealloy, thermoplastic polyurethane, silicone, or a combination thereof.14. The sensor assembly of claim 1, wherein the coating comprises aconformable material.
 15. The sensor assembly of claim 1, wherein nomoving parts of the frame remain exposed from the coating.
 16. Thesensor assembly of claim 1, wherein the unitary sensor assembly isconfigured to move between at least two mechanically stableconfigurations.
 17. The sensor assembly of claim 16, wherein the unitarysensor assembly is configured to move between the at least twomechanically stable configurations when a resistance provided at leastpartially by the resistance-providing component is overcome.
 18. Thesensor assembly of claim 1, wherein the sensor assembly is fluid tight.19. The sensor assembly of claim 1, wherein the coating is chemicallybonded to the frame.
 20. The sensor assembly of claim 1, comprising apulse oximeter monitor configured to receive data from the unitarysensor assembly.
 21. The sensor assembly of claim 1, comprising amulti-parameter monitor configured to receive data from the unitarysensor assembly.
 22. The sensor assembly of claim 1, comprising at leastone integrated circuit device.
 23. The sensor assembly of claim 1,comprising a cable comprising one or more integrated circuits.
 24. Thesensor assembly of claim 1, comprising an adapter cable connected to oneor more signal transmission structures of the unitary sensor assembly.25. The sensor assembly of claim 1, wherein the coating comprises one ormore regions configured to allow at least one of the emitter or thedetector to be displaced relative to a substantially rigid portion ofthe frame upon placement of the unitary sensor assembly on a patient.26. The sensor assembly of claim 1, wherein the resistance-providingcomponent biases the unitary sensor assembly open in a firstconfiguration and biases the unitary sensor assembly closed in a secondconfiguration.
 27. The sensor assembly of claim 1, wherein the emittercomprises one or more light emitting diodes.
 28. The sensor assembly ofclaim 1, wherein the detector comprises a photodetector.